1. Field of the Invention
The present invention is directed to an electromagnetic or electrodynamic shockwave source for generating acoustic shockwaves, of the type having a movable element which is driven for generating shockwaves, and a stationary element in electromagnetic interaction with the movable element for driving the movable element.
2. Description of the Prior Art
Electromagnetic or electrodynamic shockwaves wherein the shockwaves are generated by a movable element driven by electromagnetic interaction with a stationary element, are used in medical technology, for example for the non-invasive disintegration of calculi, for treating pathological tissue conditions, or for treating bone conditions. Such a shock wave source is disclosed in European Application 0 188 750, corresponding to U.S. Pat. No. 4,697,588. The shockwave source disclosed therein has a coil arrangement which serves as the stationary element, and which is attached to an insulator member in the shockwave source. A membrane of electrically conductive material is employed as the movable element, and is disposed opposite the stationary coil arrangement. When the coil arrangement is charged with a high-voltage pulse, currents are induced in the membrane in a direction opposite to the direction of the current flowing in the coil arrangement. As a consequence of the opposite magnetic fields arising due to the respective flows of current in the coil arrangement and in the membrane, the membrane is subjected to repelling forces which suddenly and rapidly move the membrane away from the coil. A pressure pulse is thereby introduced into an acoustic propagation medium disposed adjacent the membrane. This pressure pulse intensifies during its path through the propagation medium to form a shockwave, as a consequence of the non-linear compression properties of the propagation medium. For simplicity, the waves in the propagation medium will always be referred to herein as shockwaves, and this term will encompass incipient shockwaves in the form of pressure pulses.
When necessary, the shockwaves are concentrated onto a focal zone using suitable focusing means, for example an acoustic lens, or by shaping the shockwave source by fashioning the membrane and the coil arrangement as a portion of a sphere. The shockwave source and the subject to be acoustically irradiated are acoustically coupled to each other in a suitable manner, and are aligned relative to each other so that the region to be acoustically irradiated is situated in the focal zone.
In known shockwave sources of this type, the coil arrangement is in the form of a spiral coil, the turns of the spiral coil being connected to an insulator member by gluing. The glued connection between the coil and the insulator member is subjected to high mechanical stress, because pressure waves are also generated in the insulator member as a consequence of the repelling forces acting between the coil arrangement and the membrane when the shockwaves are generated. These pressure waves are reflected at the rear side of the insulator member, facing away from the coil arrangement, with an inversion of the operational sign, as rarefaction (i.e., negative pressure) waves. There is therefore the risk that the coil arrangement will become detached from the insulator member, which has the consequence of heat elimination from the coil into the insulator member being disrupted, and only shockwaves having largely diminished peak pressure can then be generated. Moreover, there is the risk that the coil arrangement and the membrane will be destroyed due to punctures caused by electrical arcing in the event of a detachment of the coil arrangement from the insulator member.